Low engine load conditions, e.g. engine start-up and idle at traffic lights or other vehicle waiting periods, are the periods of greatest fuel and combustion inefficiency, and produce relatively more CO, NO.sub.x and exhaust gases for the fuel used.
I.C. engines having one or more gas-exchange valves operated by excitation (energization) or de-energization of electromagnets, are known in the art. Examples are found in West German Patent Disclosure DE No. 30-24-109 (corresponding to U.S. Pat. No. 4,455,543 of Pischinger et al), and East German Patent Disclosure DE No. 35-00-530 (of Hauer et al., Binder Magnete GmbH). By switching an electromagnet off, an anchor plate connected to the gas exchange valve is released by the electromagnet and is moved away from the magnet core by spring force. In the mid-position between opposed electromagnets, the anchor plate is stressed (acted on) by springs on both sides. The anchor plate continues to move due to the initial spring push and the momentum obtained, until it moves near the opposing electromagnet, where an appropriate control energizes the open position electromagnet, ensuring that the anchor plate is captured and retained in the valve-open position. For closing, the same process is performed in reverse order.
The state-of-the-art methods require that the gas-exchange valve is held for defined periods of time in its open and closed positions, and the valve leaves its closed position only as the result of an appropriate control pulse to the electromagnet, e.g., de-energization of the closed position electromagnet.
In addition, in the state-of-the-art standard camshaft (pushrod) engines, at the phase when the inlet valve opens, the angular position of the camshaft is the same regardless of load and the timing of opening begins even before top dead center (TDC). The valve remains open through the entire downward motion of the piston, the so-called intake stroke. The inlet valve is closed about 35 degrees to 90 degrees after TDC. The quantity of gas filling the cylinder in this manner is controlled by the position of the throttle flap. By the nature of an engine in which valves are controlled by cams, the valve opening time cannot be varied in response to varying loads, RPM, etc. Designing the cam for best operation including early valve opening time at high loads means there is low efficiency at low loads.
The state-of-the-art I.C. engines having electromagnet-controlled gas-exchange valves can be operated in principle without the throttle flap. But the difficulty is that the spring system must be of very rigid (stiff) design to provide rapid response characteristics of releasing the anchor plate from the magnet. But it is not possible to make the springs relatively stiff enough (a cam and pushrod being "infinitely" stiff) so that at idle or low load requirements, the opening times of the inlet valve are sufficiently short to allow only small fuel-air mixtures to enter. Indeed, providing stiffer springs can increase the need for larger magnets to cancel the spring force when the anchor plates are captured and held. Yet larger magnets have greater delay in anchor plate release requiring even stiffer springs to obtain the necessary rapid response. This vicious circle, and the limited space available, puts natural limits on electromagnet control of valve operation during all phases of engine operation especially at low load conditions.
Accordingly, there is a great need in the art to provide better control of valves to improve fuel efficiency and reduce pollution at low load conditions.